Aerosolized medicaments are used to treat patients suffering from a variety of respiratory ailments. Medicaments can be delivered directly to the lungs by having the patient inhale the aerosol through a tube and/or mouthpiece coupled to the aerosol generator. By inhaling the aerosolized medicament, the patient can quickly receive a dose of medicament that is concentrated at the treatment site (e.g., the bronchial passages and lungs of the patient). Generally, this is a more effective and efficient method of treating respiratory ailments than first administering a medicament through the patient's circulatory system (e.g., intravenous injection). However, may problems still exist with the delivery of aerosolized medicaments.
Patients who cannot breathe normally without the aid of a ventilator may only be able to receive aerosolized medicaments through a ventilator circuit. The aerosol generator should therefore be adapted to deliver an aerosol through the ventilator. Unfortunately, medicament delivery efficiencies for combination nebulizer-ventilator systems are quite low, often dropping below 20%. The ventilator circuits typically force the aerosol to travel through a number of valves, conduits, and filters before reaching the patient's mouth or nose, and all the surfaces and obstacles provide a lot of opportunity for aerosol particles to condense back into the liquid phase.
One problem is that conventional aerosolizing technology is not well suited for incorporation into ventilator circuits. Conventional jet and ultrasonic neublizers normally require 50 to 100 milliseconds to introduce the aerosolized medicament into the circuit. They also tend to produce aerosols with large mean droplet sizes and poor aerodynamic qualities that make the droplets more likely to form condensates on the walls and surfaces of the circuit.
Delivery efficiencies can also suffer when aerosols are being delivered as the patient exhales into the ventilator. Conventional nebulizers deliver constant flows of aerosol into the ventilator circuit, and the aerosol can linger, or even escape from the circuit when the patient is not inhaling. The lingering aerosol is more likely to condense in the system, and eventually be forced out of the circuit without imparting any benefit to the patient.
The failure of substantial amounts of an aerosolized medicament to reach a patient can be problematic for several reasons. First, the dosage of drug actually inhaled by the patient may be significantly inaccurate because the amount of medication the patient actually receives into the patient's respiratory system may vary with fluctuations of the patient's breathing pattern. Further, a significant amount of drug that is aerosolized may end up being wasted, and certain medications are quite costly, thus health-care costs are escalated.
Some of the unused medication may also escape into the surrounding atmosphere. This can end up medicating individuals in proximity to the patient, putting them at risk for adverse health effects. In a hospital environment, these individuals may be health-care providers, who could be exposed to such air pollution over a prolonged period of time, or other patients, who may be in a weakened condition or otherwise sensitive to exposure to unprescribed medications, or an overdose of a medication.
For these reasons, it's desirable to increase the aerosol delivery efficiencies of nebulizer-ventilator systems. Embodiments of the present invention address these and other problems with conventional systems and methods of treating patients with aerosolized medicaments.